High pressure seal

ABSTRACT

A seal is formed between two parts of a high pressured chamber by means of a rigid ring ( 13 ), which is formed with curved surfaces ( 17 ), that engage with an anvil ( 14 ) and an enclosure part ( 10 ), the anvil ( 14 ) having a similar curved projection ( 18 ). At least one of the engaging surfaces is coated with a soft metal e.g. silver.

This invention relates to high pressure seals and in particular, but notexclusively, when such seals are being formed between two rigidelements.

There are a number of occasions in which it is necessary to form sealsbetween two engaging metal faces which are being pressed together, butwhich are subject to significant fluid pressure which is acting in asense to urge them apart. It is often desirable that these seals aremade and remade over a large number of cycles. Previous seals have useda grease such as a silicone based vacuum grease to lubricate the wearsurfaces. Such grease is also used when O-rings are provided. In certaininstances this grease is undesirable, because cleaning and regressingcan be needed on a regular basis causing down time of apparatus.

One example of such a sealing arrangement is described in EuropeanPatent Application No. 9292023.4 wherein a high pressure chamber isbeing used to process semiconductor wafers. A particular requirement ofsuch an arrangements is that the levels of particulate material must bekept to a minimum.

From one aspect the present invention consists in a vacuum or highpressure reusable seal formed between two engaging parts of rigidelements comprising, a coating of a soft metal over at least one of theengaging parts and means for urging the parts together.

The rigid elements may be formed of steel or aluminium. The seal mayinclude an underlayer, which may, far example, be nickel. Thatunderlayer may be approximately 2 μm thick. The coating may be between15 μm and 20 μm thick.

The coating may be gold, silver, platinum, palladium copper, lead orindium, or a combination of these. However, materials such as gold andcopper diffuse quite readily into semiconductor materials such assilicon or gallium arsenide and so if the seal is being used inassociation with a machine for processing such materials, those metalsmay not be appropriate.

A particularly preferred coating is silver and this coating is suitablefor use with semiconductor materials.

The invention also includes a high pressure chamber formed by twoclosable portions and a seal as defined above.

Although the invention has been defined above, it is to be understood itincludes any inventive combination of the features set out above or inthe following description.

The invention may be performed in various ways and specific embodimentswill now be described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a vertical cross-section through a machine of the typedescribed in European Patent Application No. 9292023.4;

FIG. 2 is a detail at A of the seal of that apparatus; and

FIG. 3 is a corresponding view of a seal utilising seal of theinvention.

The apparatus will not be described in detail, but instead thedisclosure of European Patent Application No. 9292023.4 is incorporatedfor that purpose. However, essentially, two enclosure parts 10, and 11,are forced together to form a chamber 12 between them in whichsemiconductor wafers be processed. As can be seen in FIG. 2 five sealinginterfaces occur between the enclosure part 10 and the enclosure part11. The first seal is formed between a gasket 16 and the upper enclosurepart 10. A rigid ring 13 forms seals with the gasket 16 and, at 15, withan anvil 14. The anvil 14 is secured to the lower enclosure part 11 anduses an O-ring to provide a seal between the anvil and the enclosurepart 11.

Turning to FIG. 3, it will be seen that the rigid ring 13 is now formedwith curved surfaces 17 and 19 that engage with the anvil 14 and theenclosure part 10 and the anvil 14 has a similar curved projection 18 inplace of the O-ring. It has been found that such engagement shapes arepossible if at least one of the engaging surfaces is coated with a soft(e.g. noble) metal, because such metals serve to lubricate the wearsurface and remove the need for the use of grease. As has been pointedout already for semiconductor wafer use, silver is particularlypreferred and attention must be given to the diffusion rates of thecoating metal into the material which is being processed.

If the metal coating is deposited by electroplating, it is desirable toprovide a nickel underlayer, but other methods of forming the coatingmay be used.

To improve the integrity of the coating, it may be desirable to coat thecomplete ring 13 or anvil 14 and it may, in some instances, beappropriate to coat both engaging surfaces, although current tests showthat a single coated surface is extremely effective.

The use of different shapes of engagement surfaces rather than linecontacts may have broad applicability.

What is claimed is:
 1. A high pressure chamber comprising upper andlower enclosures and a high pressure seal, wherein the high pressureseal is formed between two vertically aligned engaging parts of rigidelements which are secured to the upper and lower enclosures, andwherein the high pressure seal includes a coating of a noble metal overa contact surface of at least one of the engaging parts, and means forurging the vertically aligned engaging parts together in a verticaldirection only, wherein the coating is silver, and wherein the first andsecond enclosures define a semiconductor materials processing chamber.2. A chamber as claimed in claim 1, wherein the rigid elements are madeof steel or aluminium.
 3. A chamber as claimed in claim 1, wherein thecoating is between 15 and 20 μm thick.
 4. A chamber as claimed in claim1, wherein at least one of the engaging parts has a curved contactsurface.
 5. A chamber as claimed in claim 1, wherein a first of the twoengaging parts is a rigid ring member sealingly secured to the upperenclosure, and wherein a second of the two engaging parts is an anvilsealingly secured to the lower enclosure.
 6. A chamber as claimed inclaim 1, wherein the high pressure seal further includes an underlayerbeneath the coating of the noble metal.
 7. A chamber as claimed in claim6, wherein the underlayer is nickel.
 8. A chamber as claimed in claim 7,wherein the underlayer is approximately 2 μm thick.
 9. A chamber asclaimed in claim 6, wherein the underlayer is approximately 2 μm thick.10. A chamber as claimed in claim 9, wherein the coating is between 15and 20 μm thick.